python/makeproject: set appropriate build jobs count depending on the number of CPUs

python/build/makeproject.py

-import subprocess
+import subprocess, multiprocessing
 
 from build.project import Project
 
@@ -10,7 +10,12 @@ class MakeProject(Project):
         self.install_target = install_target
 
     def get_simultaneous_jobs(self):
-        return 12
+        try:
+            # use twice as many simultaneous jobs as we have CPU cores
+            return multiprocessing.cpu_count() * 2
+        except NotImplementedError:
+            # default to 12, if multiprocessing.cpu_count() is not implemented
+            return 12
 
     def get_make_args(self, toolchain):
         return ['--quiet', '-j' + str(self.get_simultaneous_jobs())]